P4/ZZ3: Joint Session: Carbon Nanomaterials for Bio-applications
Chair: Ian D. Sharp
- Tuesday PM, April 2, 2013
- Moscone West, Level 2, Room 2010-2012
1:30 PM - *P4.01/ZZ3.01
Novel Carbon Materials for Nano-biotechnology, Nano-electronics and Energy Applications
, Stanford, Stanford, California, USA.Show Abstract
This talk will present our work on carbon nanotubes, graphene nanoribbons and graphene-metal oxide hybrid materials. Biological applications of carbon nanotubes will be discussed including a new fluorescence imaging method in the so called NIR-II region in the spectral window of 1000-1400nm. NIR fluorescence enhancement of carbon nanotubes and organic fluorophores will be presented on a novel plasmonic substrate. I will then talk about graphene nanoribbons, including several methods recently developed in our lab to form high quality graphene nanoribbons with narrow widths and smooth edges. Lastly, I will talk about our recent work on making nanoparticles and nanocrystals on graphene sheets for energy storage and photocatalytic applications.
2:00 PM - P4.02/ZZ3.02
Exploring the Electronic Performance of Graphene FETs for Bio-sensing
Walter Schottky Institut, Technische Universität München, Garching, Germany; 2,
Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.Show Abstract
For medical applications such as neuroprostheses and for fundamental research on neuronal communication, it is of utmost importance to develop a new generation of electronic devices which can effectively detect the electrical activity of nerve cells. Due to its maturity, most of the work with field effect transistors (FETs) has been done based on Si. However, the high electronic noise and relatively low stability associated to Si technology have motivated the search for more suitable materials. In this respect, the outstanding electronic and electrochemical performance of graphene holds great promise for bioelectronic applications. For instance, we have reported on arrays of CVD-grown graphene solution-gated FETs (SGFETs) for cell interfacing , demonstrating their ability to transduce with high resolution the electrical activity of individual electrogenic cells .
In this contribution, we will present a detailed discussion on the sensitivity of graphene SGFETs for in-electrolyte operation, together with a study of the electrolyte composition on the device performance. The sensitivity of SGFETs is dominated by two characteristic parameters: transconductance and electronic noise. The transconductance specifies how an initial gate voltage signal is converted to a current by the transistor. For graphene SGFETs, the transconductance is proportional to the interfacial capacitance at the graphene/electrolyte interface as well as the charge carrier mobility. We will present Hall-effect experiments performed in electrolyte demonstrating that both interfacial capacitance and carrier mobility in graphene are superior to other competing materials, including Si. A second relevant parameter to assess the performance of biosensors is the electronic noise of the device, as it defines the minimum signal that can be detected. We have investigated the electronic noise of graphene SGFETs and compared it to that of devices based on Si. It will be shown that, similarly to other semiconductors, 1/f noise is the dominant noise source in graphene devices. The origin of the 1/f noise will be discussed in this presentation, comparing the results of single-layer graphene and bilayer graphene devices. Finally, we will briefly report on the pH and ion sensitivity of graphene devices, and the influence of the chosen substrate for the device fabrication, as well as of surface contamination from the fabrication technology.
This work highlights the potential of graphene to outperform state-of-the-art Si-based devices for biosensor and bioelectronic applications .
 Dankerl et al., Adv. Funct. Mater., 20 (2010) 3117
 Hess et al., Adv. Mater., 23 (2011) 5045
 C. Schmidt, Nature 483 (2012) S37
2:15 PM - P4.03/ZZ3.03
Oxide-on-graphene Bio-ready Field Effect Sensors
Physics, Penn State University, University Park, Pennsylvania, USA; 2,
Chemistry, Penn State University, University Park, Pennsylvania, USA.Show Abstract
Nanoelectronics-based detection schemes offer promising sensitive and label-free alternatives to bioanalysis. The large-scale synthesis, high carrier mobility and ambipolar transport make graphene potentially useful in the electrical detection of biomolecular targets. Here we report on the design, fabrication, and operation of novel oxide-on-graphene, bio-ready field effect sensors using graphene sheets synthesized by chemical vapor deposition. Our design uses thin layers of HfO2 and SiO2 films to isolate the graphene channel and electrodes from electrolyte and uses the top SiO2 surface for detection and further chemical functionalization. This design preserves the excellent transport characteristics of the graphene transducer while taking advantage of the well-established surface chemistry of SiO2 in facilitating specific biomolecular binding. The graphene transducer channel operates in solution with high stability and high carrier mobility of approximately 5000 cm2/Vs. By applying the solution gate voltage in pulse, we eliminate hysteresis in the transfer curve of the graphene channel, which is critical to achieving a high detection resolution of the sensor. We demonstrate the silanization of the SiO2 surface with aminopropyl-trimethoxysilane (APTMS), which can be further linked to biomolecular probes and targets. The pH sensitivity of the bare and APTMS-functionalized SiO2 is measured to be 46mV/pH and 43mV/pH respectively, in good agreement with literature results. With suitable linking chemistry, these graphene sensors can potentially be useful in the detection of biological events such as DNA hybridization, thus opening a new avenue for biosensing using nanoscale electronics.
2:30 PM - P4.04/ZZ3.04
Graphene for Biosensing and Surface Functionalization
, Naval Research Lab, Washington, District of Columbia, USA.Show Abstract
Graphene, a one-atom thick sheet of sp2 carbon, offers many intriguing possibilities in the field of molecular sensing. Its unique combination of large areas with nanometer thickness and high electrical conductivity could enable small scale device sensitivity with large scale production methods. A major benefit of using graphene is the large toolbox of well-established chemistries for incorporating chemical functionalities or specific recognition elements at the device surface. Here, we will discuss our efforts to develop graphene-based biological field-effect transistors (BioFETs), which offer sensitivity comparable to sensors made with other nanoscale materials (carbon nanotubes, nanowires), but with greatly simplified production methods common in the semiconductor industry. Devices utilizing both graphene and graphene oxide will be covered, and surface spectroscopic studies of the material modification will be discussed. Successful results for the detection of specific DNA hybridization using graphene BioFETs will also be presented. We will further discuss our efforts to use graphene as a biofunctionalized interface for a number of materials, from polymers to dielectrics to semiconductors, of interest to the biosensing community. Graphene’s ultrathin nature allows its inclusion in more traditional sensing platforms as a non-intrusive functionalization layer, discreetly lending its chemical flexibility to other, more inert materials without significantly impacting the sensing device.
2:45 PM - P4.05/ZZ3.05
Reduced Graphene Oxide Micropatterns for Biosensor Applications
Delle1 2, Ruben
Lanche1 2, Maryam
Informatics and Microsystem Technology, University of Applied Sciences Kaiserslautern, Zweibruecken, Germany; 2,
Institute for Materials Research, Hasselt University, Diepenbeek, Belgium.Show Abstract
Graphene has been identified as a promising material for different scientific disciplines due to its exceptional physiochemical, electronic and structural properties. The extremely high carrier mobility and capacity arouses enormous interest in the field of electronic sensor applications as well. However, it is a challenge to obtain constantly small size of graphene layers by mechanical exfoliation. In the present study, grapheme oxide (GO) was used as the transducer material for two different biosensor platforms:
In a first approach, interdigitated gold microelectrodes (IDEs) were fabricated with standard lithographical methods and used as a platform for label-free detection of specific DNA hybridization and denaturation events. GO flakes were dielectrophoretically immobilized onto the IDEs and reduced to conductive graphene oxide (r-GO) using a low-temperature, green fabrication route with L-ascorbic acid (Laa). These sensors were used for label-free, impedimetric detection of DNA hybridization and denaturation. This approach is very versatile and could be applied to different substrates such as polymeric materials, since this green fabrication route doesn’t need harsh chemicals or elevated temperatures.
In a second approach, the ‘Micromolding in Capillaries’ (MIMIC) technique was used to pattern GO lines with lengths up to 10 mm and width down to 10 µm on glass and Si/SiO2 substrates. The GO patterns were then reduced to r-GO using the same approach mentioned above. The lines were connected by evaporated gold contacts and encapsulated to be used with living cells for in vitro monitoring of cellular adhesion of tumor cells and for detection of extracellular field potential (exFP) of cardiac cells. We found that cells preferably aligned to the r-GO lines in contrast to the bare glass or SiO2 surfaces. The patterns can be used for the definition and stabilization of networks of neuronal cells on in vitro sensor platforms. Since in a typical application in this field, the transducer material of microelectrode arrays (MEAs) is made of metal and subsequently functionalized with cell growth supporting proteins such as laminin or fibronectin, our r-GO approach has the advantage that the transducer material and the cell adhesion promoting material is the same.
In conclusion it can be said that the r-GO material, even though it has distinctly reduced electrical performance compared the single sheets of graphene, has promising properties, which make it a favorable transducer material in biosensor applications.
3:00 PM -
3:30 PM - P4.06/ZZ3.06
Clean Transfer of CVD Graphene for Biomolecule-graphene Nanosandwiches
Wood1 2 3, Gregory
Doidge1 2 3, Justin
Koepke1 2, Enrique
Carrion1 3, Gregory
Damhorst3 4, Eric
Salm3 4, Rashid
Bashir1 3 4, Eric
Pop1 2 3, Joseph
Lyding1 2 3.
Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA; 2,
Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA; 3,
Micro and Nanotechnology Lab, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA; 4,
Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.Show Abstract
Graphene’s planar, conformal, and hydrophobic nature make it useful as an atomically thin coating which inhibits gaseous diffusion  and entraps liquids [2,3]. Most studies to date have only explored encapsulation of simple molecules with graphene, overlooking interactions between the hydrophobic sheet and other complex nanostructures like DNA and viruses.
We develop an atomically clean graphene transfer process using a poly(bisphenol A carbonate) (PC) scaffold for graphene grown by chemical vapor deposition (CVD). Large-area CVD graphene growth on Cu [4,5] allows the fabrication of large-area, conductive, encapsulating platforms between graphene and nanostructures of choice. Typically, graphene is transferred off the Cu growth surface in H2O  with a PMMA scaffold, and this scaffold is partially removed by a high-temperature anneal . However, such high-temperature processing is incompatible with biomolecular nanostructures. PC transfers can be removed by dissolution at room-temperature, circumventing the annealing requirement. We confirm that the clean, PC-transferred graphene films have lowered residual doping by device transport and Raman spectroscopy. RMS roughness values, determined by atomic force microscopy (AFM), are 2-4 times lower (~0.6 nm) for PC- vs. PMMA-transferred films under the same growth and transfer conditions. Scanning tunneling microscopy (STM) of the PC-transferred graphene films reveals atomic resolution, despite degas temperatures lower than 100 °C.
Using the PC transfer process, we make graphene/biomolecule/graphene nanosandwiches on SiO2/Si and mica. We deposit a known rod-shaped biomolecule, the tobacco mosaic virus (TMV), on these substrates and examine the virions’ heights before and after graphene-based encapsulation. With AFM, we find that the TMV heights, relative to the top-most graphene layer, decrease from 12.4 nm to 3.5 nm after encapsulation. These deformations occur despite the rigid TMV capsids. Here, the graphene conforms to the virions and exhibits a strong hydrostatic pressure on them, flattening and possibly dehydrating the capsid shell. Through AFM topographs, we determine that nanosandwiched TMV denatures at ~50 °C, much higher than the known value at ~42 °C . The graphene/biomolecule/graphene system will elucidate fundamental fluid dynamics in this hydrophobic bilayer cell. Additionally, the conductive and electronically transparent character of graphene can allow biomolecular interrogation at the atomic-level by STM and by transmission electron microscopy.
 J. S. Bunch et al., Nano Lett. 8, 2458 (2008);  K. T. He et al., Nano Lett. 12, 2665 (2012);  J. M. Yuk et al., Science 336, 61 (2012);  X. Li et al., Science 324, 1312 (2009);  J. D. Wood et al., Nano Lett. 11, 4547 (2011);  Y.-C. Lin et al., ACS Nano 5, 2362 (2011);  M. Kelve et al., J. Biomol. Struct. Dyn. 5, 105 (1987).
3:45 PM - P4.07/ZZ3.07
Ion Transport in Carbon Nanotube Ion Channels
Kim1 2, Jia
Geng2 3, Ramya
Tunuguntla2 4, Costas
Noy2 3 5.
, University of California at Berkeley, Berkeley, California, USA; 2,
, The Molecular Foundry at Lawrence Berkeley National Laboratory, Berkeley, California, USA; 3,
, University of California at Merced, Merced, California, USA; 4,
, University of California at Davis, Davis, California, USA; 5,
, Lawrence Livermore National Laboratory, Livermore, California, USA.Show Abstract
Carbon nanotubes (CNT) are a promising biomimetic material, in part because smooth, narrow and hydrophobic inner pores of CNT are remarkably similar to the natural biological pores. Incorporation of nanotube channels into the biologically-relevant environments and measurements of ion transport in these assemblies would not only enhance out understanding of transport in these materials systems, but also open up ways to develop novel bioengineering applications. We will describe incorporation of carbon nanotube channels into a lipid membrane and measurement of osmotically-induced ion transport through these model nanopores using dynamic light scattering (DLS) experiments. We also discuss factors that govern ion rejection in these structures and compare the results with modeling results and measurements in macroscopic systems.
4:00 PM - *P4.08/ZZ3.08
Functional Carbon Interfaces
Department of Chemical and Pharmaceutical Sciences, University of Trieste, Trieste, Italy.Show Abstract
Nanometer-scale structures represent a novel and intriguing field, where scientists and engineers manipulate materials at the atomic and molecular levels to produce innovative materials for composites, electronic, sensing, and biomedical applications. Carbon nanomaterials, such as carbon nanotubes and graphene, constitute a relatively new class of materials exhibiting exceptional mechanical and electronic properties, and are also promising candidates for gas storage and drug delivery.
However, processing carbon nanotubes is severely limited by a number of inherent problems: purification from a variety of byproducts, difficult manipulation and low solubility in organic solvents and in water are only some of these problems. For these reasons, several strategies have been devised to make nanotubes “easier” materials. In particular, organic modification produces functionalized carbon nanotubes, which are much more processible and offer the possibility of introducing organic fragments useful for practical applications.
During this talk, we will discuss the use of functionalized carbon nanotubes and graphene as active surfaces for a number of practical applications. Glassy surfaces, covered with carbon nanotubes are ideal substrates for neuronal growth. Nanotubes are compatible with neurons, but especially they play a very interesting role in interneuron communication, opening possibilities towards applications in spinal cord repair therapy.
In addition, in combination with catalysts of different nature, carbon nanotube modified surfaces can serve for many scopes. Experiments aiming at the splitting of water to give oxygen, and therefore, molecular hydrogen, ideal for clean energy generation, will be described. Also, multiwalled carbon nanotubes, embedded inside mesoporous layers of oxides (TiO2, ZrO2, or CeO2), which in turn contain dispersed metal nanoparticles (Pd or Pt), result in nanocomposites with remarkable performance in catalytic reactions.
(1) Fabbro, A.; Bosi, S.; Ballerini, L.; Prato, M. ACS Chem. Neurosci. 2012, 3, 611-618.
(2) Toma, F. M.; Paolucci, F.; Prato, M.; Bonchio, M. et al. Nature Chemistry 2010, 2, 826-831.
(3) Cargnello, M.; Liz-Marzan, L. M.; Gorte, R. J.; Prato, M.; Fornasiero, P. et al. J. Am. Chem. Soc. 2012, 134, 11760-11766.
4:30 PM - P4.09/ZZ3.09
Effects of Carbon Nanotube Patterning on Charge Injection for Neural Stimulation
Electrical and Computer Engineering, Duke University, Durham, North Carolina, USA; 2,
Biomedical Engineering, Duke University, Durham, North Carolina, USA; 3,
, RTI International, Durham, North Carolina, USA.Show Abstract
Functional electrical stimulation can be used to restore function in patients with a damaged nervous system. Electrical impulses delivered to the tissue can generate artificial action potentials (APs) that behave like APs naturally generated by a healthy nervous system. These APs will have the same effects and will propagate through neighboring neurons to induce motor function. Electrode morphology can impact the charge injection for neural stimulation as shown in literature reports on the electrochemical properties of vertically aligned multi-walled carbon nanotubes (CNTs), graphenated CNTs, and nanoribbons. For example, the roughness of carbon nanotubes increases the surface area of the electrode and in turn, decreases the impedance and power consumption.
In the present work, patterned CNTs were grown with the goal of improving the charge injection in two ways. The pores created by the roughness of the CNT structure may be too small for the ions in the electrolyte to penetrate. The patterns should increase the total surface area accessible by the ions. In addition, the activating function for neural cells is proportional to the spatial derivative of the current density in the tissue. When an electric potential is applied across a structure, the current density is higher at the edges. The patterns should also increase the total perimeter contributed by the array of pillars. By varying the dimensions of the pillared CNT structures, the total surface area accessible by the ions and the number of edges can be increased in order to achieve a maximum charge injection while simultaneously decreasing the impedance. A model of the pillared CNT structures was created in COMSOL. The optimal dimensions for the pillars were then chosen from the parameters that resulted in the most non-uniform current density. The electrochemical properties of the best structures were then characterized in vitro. Cyclic voltammetry was used to detect the presence of reactions with the electrolyte. Electrochemical impedance spectroscopy was used to measure the electrode-electrolyte interfacial impedance. Finally, potential transient measurements were used to measure the charge injection capacity of the electrode. It was observed that the charge injection of the CNT electrodes was not dependent on the total volume of the structure but was greatly affected by the surface area and the total edge contribution from the pillars. As both of these parameters were increased, the charge injection increased. The pillared structures with optimized aspect ratios had the highest charge injection compared to normal blanket CNT, graphenated CNT, and nanoribbon electrodes.
4:45 PM - P4.10/ZZ3.10
All-carbon Diamond Micro-electrode Arrays for Neural Interfacing
Institute for Material Research, Hasselt University, Diepenbeek, Belgium; 2,
IMOMEC, IMEC vzw, Diepenbeek, Limburg, Belgium; 3,
Biomedical Science, University of Antwerp, Antwerp, Belgium.Show Abstract
CVD Diamond thin-films are attractive as a material for construction of active bio-electronic devices. This is due to properties of Nano-crystalline diamond such as biocompatibility, wide potential window and substantially reduced bio-fouling or inflammatory reactions.
Here we present a novel approach for fabrication of all-carbon diamond Micro-electrode Arrays (MEAs) in which Nano-crystalline diamond (NCD) thin film represents the insulating layer and Boron-doped Nano-crystalline diamond (B-NCD) features conductive layer of the electrode as a replacement for conductive metals, such as Platinum or Titanium Nitride, with B-NCD showing better electrochemical performances. The resulting MEAs are optimized and characterized in terms of their performances and impedance, and employed in vitro for recording/stimulation of neuronal electrical activity. The measurements are carried out using cultured dissociated neurons and compared with standard commercial MEAs to benchmark metallic MEA with full diamond MEA in the application of active neuron-device interface. The signal to noise ratio is evaluated and compared to results obtained by Dankerl et al. , showing higher signal to noise ratio in comparison to conventional metal MEAs.
 M. Bonnauron et al., phys. stat. sol. (a) 205, No. 9, 2126-2129 (2008).
 M. Dankerl, et al., Appl. Phys. Lett. 100, No. 2, 023510 (2012).
P5: Poster Session: Synthesis, Characterization, and Properties
- Tuesday PM, April 2, 2013
- Marriott Marquis, Yerba Buena Level, Salons 7-8-9
8:00 PM - P5.04
Carbon Nanotubes Growth on Metal Vapor Phase Impregnated Surfaces: A Novel One-step Approach
, CRP Gabriel Lippmann, Belvaux, Luxembourg.Show Abstract
Carbon nanotubes (CNTs) can be grown on a variety of predefined sites as demonstrated by the catalytic chemical vapor deposition (CCVD) process which uses to thermally decomposed short-chain hydrocarbons over metal catalysts. This elaboration method ensures less unwanted carbon products as fibers or soot. It is well reported that the length, the diameter and the growth density of CNTs is related to the morphology of the catalyst particles, this approach needs a precise tunability of the particles morphology (size, shape, density). Apart from the commonly used catalytic growth, impregnated template-free supports with liquid metal-acetylacetonates (Me(acac)2) can be performed. Thermal treatment of impregnation layer induces the decomposition of the adsorbed precursor on the surface. Nevertheless, the incorporation of Me(acac)2 into organic solvent increases the global carbon feedstock present during the CNTs growth step. Furthermore the liquid impregnation method might be very challenging in the cases of hydrophobic surfaces. To overcome those issues, we propose to investigate the efficiency of metal-acetylacetonates vapor phase impregnation, with a particular focus on Co(acac)2.
The effects of various processing parameters such as exposure time, pressure and temperature were particularly studied. From the hypothesis that the one-step CNTs growth is driven by the thermal decomposition of acetylene on Co-riched phases, the temperature, the time of reaction, the acetylene/hydrogen ratio and the H2 annealing pre-step are critical parameters tailoring the Co-phases properties and their dynamic interactions with the short-chain hydrocarbons. The samples are deeply characterized to relate the gas-phase chemistry reaction to the density and the rate of nanotubes growth. CNTs and Co-phases are characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD).
In addition, the suitability of the gas-phase impregnation process to 3D substrates such as microparticles using fluidized bed vapor phase reactor is reported.
8:00 PM - P5.05
Carbon Nanotube Growth and Structure at Low Growth Temperatures
, Sandia National Laboratories, Albuquerque, New Mexico, USA.Show Abstract
Carbon nanotubes (CNTs) are grown by thermal chemical vapor deposition, and their structure is studied as a function of the reduction and growth temperatures. During the reduction stage, the temperature must sufficient for oxygen to be removed from the catalyst layer by the reducing gas, and during the growth stage the temperature is used to crack the hydrocarbon feed gas to produce CNTs. Previously we demonstrated growth of straight, high crystalline quality CNTs on 2.5 nm thick Ni catalyst on W-coated Si (100) from 350 °C to 600 °C with a constant CO reduction at 600 °C. The highest temperature seen during the process appears to control the inner core diameter, which is ~ 1 nm for the above mentioned CNTs. This relationship is further explored in this work by lowering both the reduction and growth temperatures so that the highest temperature seen by the catalyst can be independently set. The resulting inner and outer wall diameters, number of walls, and crystalline quality are studied by high resolution transmission electron microscopy, and Raman spectroscopy is used to identify the chirality of single walled carbon nanotubes and the representative C-C bonding of multi-walled carbon nanotubes. The effects of the reduction and growth temperatures on CNT overall growth and structure are studied with different reduction gases including CO and NH3 and on different substrates including silicon and sapphire. The results are relevant to applications in which CNTs with specific properties are desired on substrates which cannot withstand the high temperatures normally required for high quality CNT growth.
This work is supported by the Laboratory Directed Research and Development Program at Sandia National Laboratories. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
8:00 PM - P5.06
Graphene Synthesis on Nickel : An Atomic Scale Study
Diarra1 2, Mounib
, ONERA-CNRS, Chatillon, France; 2,
, CNRS, Marseille, France.Show Abstract
Growing graphene on a metal surface is one possible way to obtain a high quality graphene, with a controllable number of layers. The synthesis usually relies on a chemical vapor deposition of a carbon bearing gas on the surface of a metal such as Ir, Cu, or Ni. We investigate the latter case of graphene on Ni that is of particular interest because the role of carbon solubility in subsurface layers is both difficult to investigate experimentally and important to understand for the production of high quality graphene.
To study the interaction of carbon with nickel at the atomic level, we have developed a tight binding model  implemented in a Monte Carlo code. It has been used to study the nucleation of carbon nanotubes in CVD processes . Using the same Grand Canonical algorithm as used in [1,3], but with significantly larger systems and better accuracy, we investigate the CVD synthesis of graphene on a Ni surface. Depending on the growth conditions, we show that variable amounts of C can be found in the subsurface layers and we correlate this to experimental data. Since the obtained graphene-like layer covering the Ni surface often presents defects (pentagons, heptagons, vacancies, …), we also numerically study the healing mechanisms of these defects that are made more efficient in the presence of the metal surface layer 
 H. Amara, J.-M. Roussel, C. Bichara, J.-P. Gaspard and F, Phys. Rev. B 79, 014109 (2009)
 M.-F. C. Fiawoo, A.-M. Bonnot, H. Amara, C. Bichara, J. Thibault-Pénisson and A. Loiseau, Phys. Rev. Lett. 108, 195503 (2012)
 H. Amara, C. Bichara and F. Ducastelle, Phys. Rev. B 73, 113404 (2006).
 S. Karoui, H. Amara, C. Bichara and F. Ducastelle, ACS Nano 4, 6114 (2010)
8:00 PM - P5.07
Importance of Carbon Solubility and Wetting Properties of Nickel Nanoparticles for SWNT Growth
Diarra1 2, Alexandre
, ONERA-CNRS, Chatillon, France; 2,
, CNRS, Marseille, France.Show Abstract
A rational control of the structure of Single Wall Carbon Nanotubes during their synthesis is highly desirable, but currently limited by our poor understanding of nucleation and growth mechanisms and the lack of direct evidence on the actual state of the catalyst particle / nanotube interface. To progress towards an atomic scale understanding, we use a carefully assessed tight binding model for nickel and carbon [1, 2] to numerically investigate different aspects of the CCVD synthesis process.
Owing to significant technical improvements of our grand canonical Monte Carlo code , we can extend our previous calculations  of carbon adsorption isotherms to nanoparticles (NPs) up to 807 Ni atoms, in a broad temperature range. We thereby study the carbon solubility and physical state of the metal catalyst as a function of size, temperature and carbon chemical potential conditions corresponding to nucleation and growth of SWNTs. Combining experimental information from Transmission Electron Microscopy and atomistic computer simulation, we try and understand the relation between the diameters of the tube and the metallic NP from which it grows . We then study the wetting of the NPs with respect to sp2 carbon walls, that strongly depends on carbon concentration, and emphasize its role in the growth of tubes. This enables us to identify conditions leading to experimentally observed situations: aborted growth by encapsulation of the metal NP with carbon, growth termination by detachment of the tube from the NP and continuous growth under mild carbon chemical potential, temperature and feeding rate conditions.
 H. Amara, J. M. Roussel, C. Bichara, J.-P. Gaspard and F. Ducastelle, Phys. Rev. B 79, 014109 (2009).
 J. H. Los, C. Bichara and R. Pellenq, Phys. Rev. B 84, 085455 (2011).
 H. Amara, C. Bichara and F. Ducastelle, Phys. Rev. Lett., 100, 056105 (2008).
 M.-F. C. Fiawoo, A.-M. Bonnot, H. Amara, C. Bichara, J. Thibault-Pénisson and A. Loiseau, Phys. Rev. Lett. 108, 195503 (2012).
 M. Diarra, A. Zappelli, H. Amara, F. Ducastelle and C. Bichara, Phys. Rev. Lett. (accepted)
8:00 PM - P5.08
Synthesis of Graphene on (6√3 × 6√3)R30° Reconstructed SiC Surfaces by Molecular Beam Epitaxy
Seyller2 3, Marcelo
, Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany; 2,
Lehrstuhl für Technische Physik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany; 3,
Institut für Physik, Technische Universität Chemnitz, Chemnitz, Germany.Show Abstract
We report on the synthesis of graphene by means of molecular beam epitaxy (MBE). This technique is widely used in semiconductor device research to produce high-quality layers on different substrates at moderate temperatures (<1000 °C). The growth by MBE does not involve catalytic processes and could in principle be extended to a large variety of substrates. In addition, one of the main advantages of MBE is that it offers the benefit of accurate deposition rates and sub-monolayer thickness precision. Therefore, MBE might enable the growth of large area graphene films (mono- and few-layer) directly on different insulating or semiconducting substrates, which is of high technological relevance for many applications. We investigated the growth of graphene on a (6√3 × 6√3)R30° reconstructed SiC(0001) surface. This surface reconstruction, also known as buffer layer, is isomorphic to graphene (i.e. it possesses the same crystal structure and similar lattice constant), however with about 30% of its atoms covalently bond to the SiC substrate. Its use as a template enables the investigation of quasi-homoepitaxy of graphene by MBE, with the advantage over the use of epitaxial graphene that the results from different analysis methods are not disturbed by contributions originated from the substrate. Graphene films have been prepared on the buffer layer at a substrate temperature of 950 °C for different growth times. The source used for atomic carbon evaporation is a high-purity pyrolytic graphite filament heated by electric current. For the utilized growth conditions no concomitant surface graphitization due to Si atoms depletion takes place. Atomic force microscopy shows that the initial SiC surface morphology with atomically smooth terraces and steps in between them is not drastically altered after MBE growth. Raman spectroscopy reveals that the quality of the MBE-grown graphene films increases with growth time and that the average crystallite size exceeds 20 nm. X-ray photoelectron spectroscopy confirms that the thickness of the films increases as a function of the growth time and additionally proves that the buffer layer is preserved during the growth process. Grazing-incidence X-ray diffraction measurements were performed at the beamline ID10 of the European Synchrotron Radiation Facility in Grenoble. Signals from the buffer layer, as well as from the MBE-synthesized graphene, were detected. Interestingly, despite its nanocrystalline nature, the graphene films grown by MBE shows an in-plane alignment to the substrate, revealing that a conventional epitaxial growth on the buffer layer takes place. The results will be discussed in the context of MBE growth of graphene considering the most recent data reported in the literature.
8:00 PM - P5.09
Selective Dispersion of Wide Diameter-range Semiconducting Carbon Nanotubes by Polyfluorene Derivatives
Costanzo2 1, Elton
Jose Figueiredo de
Carvalho3 1, Satria
, Zernike Institute for Advanced Materials, University of Groningen, Groningen, Netherlands; 2,
, Laboratorio de Procesado de Imágenes, Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; 3,
, Instituto de Física, Universidade de Sao Paulo, Sao Paulo, Brazil; 4,
, Chemistry Department and Institute for Polymer Technology, Wuppertal University, Wuppertal, Germany.Show Abstract
Conjugated polymers have been proven to be able to selectively disperse semiconducting single walled carbon nanotubes from metallic tubes. The separation using this technique has as main advantage that the physical properties of the nanotubes can be maintained due to the non-covalent interaction between the polymer chains and the carbon nanotube walls. The current state of art of this technique only allows the separation of small diameter tubes (0.8-1.2 nm). Meanwhile, larger diameter tubes, which have more prospects for high performance optoelectronic device applications still cannot be separated using this technique. Here we demonstrated the selection of small and large diameter semiconducting SWNTs (0.8 to 1.6 nm) with very effective individualization by using polyfluorene-derivatives. Polyfluorene with long alkyl side-chains showed the ability to discriminate larger diameter nanotubes. Optical spectroscopy including photoexcitation lifetime measurements allows establishing the high quality of the SWNT dispersion in term of minimal metallic content and lower nanotubes bundling.
Molecular dynamics simulations allow rationalizing the nature and mechanism of the interaction between the polymer chains and SWNTs. The simulation demonstrated that the increasing of length of the polymer side-chains increases the coverage wrapping area and the binding energy between the polymer and the carbon nanotube walls. Using these highly enriched semiconducting nanotubes dispersions, we fabricated high-performance network field effect transistors. The field effect transistors showed ambipolar properties with charge-carrier mobility higher than 10 cm2/V.s and on/off ratio more than 105 by using ion gel as the gate dielectric layer. Our finding offers a new approach to separate big diameter semiconducting carbon nanotubes allowing their use for high performance device applications.
8:00 PM - P5.10
Real-time Optical Diagnostics of Isothermal Graphene Growth Induced by Pulsed Chemical Vapor Deposition and PLD
, ORNL, Oak Ridge, Tennessee, USA; 2,
, University of Tennessee, Knoxville, Tennessee, USA.Show Abstract
Here we report real-time Raman spectroscopy, optical imaging, and reflectivity, combined with sub-second pulses of acetylene to measure the nucleation and growth kinetics of graphene on Ni films by pulsed chemical vapor deposition (CVD) and pulsed laser deposition (PLD). Despite many publications devoted to graphene growth by chemical vapor deposition (CVD) on different metals several major questions remain to be addressed. For example, in the case of metals which can dissolve carbon the contribution of surface growth versus precipitation during cool down is not clear. Also, crucial growth kinetics measurements required to understand the growth mechanisms have not been studied in real time, especially in the case of fast growth. Using pulsed gas delivery and real time optical measurements we demonstrate that a few layer, high quality graphene can be grown rapidly and isothermally at high temperatures. Using direct in situ Raman monitoring of the growth kinetics with 1s acquisition time at high temperatures (between 800-850 °C) graphene is found to grow within one second on Ni after exposure to a sub-second C2H2 pulse. Real-time Raman measurements were performed to reveal the fraction of graphene which appears during cool down as a function of the growth temperature and partial feedstock gas pressure. In addition, time-resolved reflectivity and direct video-imaging through a microscope were performed for comparison with the Raman kinetics measurements, revealing a 0.5 s delay in the onset of growth after the gas pulse. The combined approach involving pulsed feedstock delivery and real-time optical diagnostics opens new opportunities to understand and control the fast, sub-second growth of graphene on various substrates at high temperatures.
Research supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Science and Engineering Division, and performed in part at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.
8:00 PM - P5.11
Diameter Controlled Growth of Single-walled Carbon Nanotubes Using Added Oxygen
Physics and Astronomy, University of California, Irvine, Irvine, California, USA.Show Abstract
Water-assisted chemical vapor deposition (CVD) has become a standard synthesis method for high quality single-walled carbon nanotubes (SWCNTs). Some drawbacks of the water-assisted method, however, include good control of water concentrations in the feedstock and poor control of SWCNT diameters below 2.0 nm. Here, we describe a variation of water-assisted CVD that uses dry feedstocks with a small, controlled quantity of molecular oxygen. Reactions of oxygen with hydrogen in the reaction zone provide all the benefits of water-assisted growth at the substrate while maintaining dry valves and flowmeters. In addition, the oxygen-based technique allows water concentrations in the system to be varied precisely and with short time constants. Perhaps because of the improved control, we find that the SWCNT diameter can be easily tuned by changing the oxygen concentration during the growth phase. Changing the oxygen flow rate from 25 sccm to 60 sccm (in 5000 sccm of other feedstocks) varied the resulting SWCNT diameters from 1.5 to 0.5 nm, with typical diameter distributions less than +/- 30%. Control of SWCNT growth within this diameter range is ideal for probing opto-electronic properties of individual SWCNTs and SWCNT devices.
8:00 PM - P5.12
Plasma Enhanced Chemical Vapor Deposition of Single Layer Graphene at Low Temperatures
van der Laan1 2, Shailesh
Kumar2 1, Kostya (Ken)
School of Physics, University of Sydney, Sydney, New South Wales, Australia; 2,
Materials Science and Engineering, CSIRO, Sydney, New South Wales, Australia.Show Abstract
The use of graphene has the potential to improve the performance of a diverse range of advanced nanodevices, in applications ranging from nanoelectronics to ultra-sensitive environmental monitoring. Incorporation of graphene into devices requires the development of a large-scale method of fabrication of high-quality graphene, which remains a significant challenge despite years of effort. The method that shows the most promise is chemical vapor deposition (CVD), which, however, requires a high growth temperature (generally over 1100 K). Our work focuses on the development of a plasma-enhanced CVD approach to fabricate high-quality graphene at a low substrate temperature (as low as 525 K) without any external heating source. We have successfully deposited single-layer graphene on a flexible polycrystalline copper foil using an inductively-coupled plasma. Micro-Raman spectroscopy indicates that the films have thicknesses of up to three layers of graphene. Single-layer graphene crystals in the film were confirmed by imaging the graphene crystal lattice using high-resolution TEM. Further investigations revealed that the graphene grain size can be altered by controlling the delivery of carbon to the substrate surface. Graphene films transferred from copper foil to quartz exhibit transparency and resistance of ~80% and 8 kΩ, respectively. The films were tested for their biosensing properties using a standard protein, bovine serum albumin. The method of fabrication of graphene at low temperature presented in this work has marked advantages over previous growth processes, and brings the production of graphene-based devices closer.
8:00 PM - P5.15
In-situ Observations of Gas Phase Dynamics During Graphene Growth Using Solid-state Carbon Sources
Kwon1, Jae Hwan
Lee2, Sung Youb
Kim1 3, Hyung-Joon
Shin1 3, Kibog
Park4 3, Jang-Ung
Park2 3, Soon-Yong
Kwon1 3 4.
School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, Republic of Korea; 2,
School of Nano-Biotechnology and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, Republic of Korea; 3,
Opto-Electronics Convergence Group & Low Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, Republic of Korea; 4,
School of Electrical, Electronic and Computer Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, Republic of Korea.Show Abstract
Large-scale monolayer graphene has been uniformly grown on a Cu surface at elevated temperatures by thermally processing a poly(methyl methacrylate) (PMMA) film in a rapid thermal annealing (RTA) system under vacuum. The detailed chemistry of transition from solid-state carbon to graphene on the catalytic Cu surface was investigated by performing in-situ residual gas analysis while PMMA/Cu-foil samples being heated, in conjunction with Raman spectroscopy after thermal processing. The data clearly show that the formation of graphene occurs with hydrocarbon molecules vaporized from PMMA, such as methane and/or methyl radicals, as precursors rather than by the direct graphitization of solid-state carbon. We also found that the temperature for vaporizing hydrocarbon molecules from PMMA and the time for maintaining the hydrocarbon gaseous atmosphere, which are dependent on both the heating temperature profile and the amount of a solid carbon feedstock are the dominant factors to determine the crystalline quality of the resulting graphene film. Under optimal growth conditions, the PMMA-derived graphene was found to have the carrier (hole) mobility as high as ~2,700 cm2V-1s-1 at room temperature, superior to common graphene converted from solid carbon.
8:00 PM - P5.18
Single Graphene Layer as Electrode in Aqueous Electrochemical Cells: In situ XAS Study
Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA; 2,
Advance Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, USA; 3,
Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, USA.Show Abstract
Graphene is a major topic of research due to its structure, electronic, chemical, optical and mechanical properties . The high electrical conductivity as well as the chemical stability in aggressive media of graphene makes it a candidate as electrode in electrochemical applications. We investigated the stability of single graphene layers (SGL) by in-situ NEXAFS at the Advance Light Source.
We used SGL grown on copper foil by CVD using methane  and transferred onto the back side of thin (~100nm) Si3N4 membranes transparent to the X-rays. The membranes are part of the electrochemical cell and separate the cell from the vacuum chamber connected to the Synchrotron ring. Pt and Ag wires were inserted in the cell body as counter and pseudo-reference electrodes. A 2 mM electrolyte solution flowed through inlet and outlet holes and the potential was controlled with a potentiostat. Using this experimental setup, it was possible to achieve real time monitoring of the element-specific electronic structure changes during electrochemical cycling.
X-ray absorption spectroscopy (XAS) from the graphene electrode material was performed in situ during cyclic voltammetry. The shape of the C K-level peak is sensitive to the chemical structure of the absorbing atom. Our spectra proved that at positive potentials formation of carboxyl COOH groups and CO is favoured, while at negative potentials hydroxyl groups C-OH are dominant. The electrochemical potential induces also the formation of point defects at potentials below 0.5 V, and fast degradation at higher potentials, as demonstrated by ex-situ studies with AFM. The formation of numerous point defects was also corroborated by Raman measurements of the D/G peak ratio. These observations are consistent with the progressive loss of graphitic character .
 Y. Zhu, S. Murali, W. Cai, X. Li, J.W. Suk, J.R. Potts, and R.S. Ruoff, “Graphene and Graphene Oxide: Synthesis, Properties, and Applications”, Advanced Materials, Vol. 22, Iss. 35, pp. 3906-2924, 2010.
 A. Ismach, C. Druzgalski, S. Penwell, A. Schwartzberg, M. Zheng, A. Javey, J. Bokor, and Y. Zhang, “Direct Chemical Vapor Deposition of Graphene on Dielectric Surfaces”, Nano Letters, 10(5), pp. 1542-1548, 2010.
 P. Jiang, J.L. Chen , F. Borondics, P.A. Glans, M.W. West, C.L. Chang, M. Salmeron, J. Guo, “In situ soft X-ray absorption spectroscopy investigation of electrochemical corrosion
of copper in aqueous NaHCO3 solution”, Electrochemistry Communications 12, pp. 820-822, 2010.
 S. Stasio, and A. Braun, “Comparative NEXAFS Study on Soot Obtained from an Ethylene/Air Flame, a Diesel Engine, and Graphite”, Energy Fuels, 20 (1), pp. 187-194, 2006.
8:00 PM - P5.20
Giant Positive Magnetoresistance Devices Based on Metal-oxide Covered Graphene
Zhu1, Kwok Kwong
Physics Department, Hong Kong University of Science and Technology, Hong Kong, Hong Kong.Show Abstract
Several innovative techniques have been employed for the new generations of magnetoresistance (MR) devices including spin valves at heterojunctions (GMR), metal-insulator transitions driven by magnetic fields (CMR) and geometrical inclusions (EMR). We developed a very simple but effective method to fabricate large positive MR devices based on single layer graphene (SLG): an ultrathin layer of metal atoms is deposit on top of SLG and followed by oxidation on hotplate for 15 minutes. These SLG devices are promising candidates for magnetic sensors, which exhibit large positive MR up to 200% for B=2T and 600% for B=8T at cryogenic temperatures. Graphene’s extraordinary electronic properties such as high mobility (~20000 cm2/Vs) and Landau level quantization have been well preserved even capped with these oxide layers. Strong temperature sensitivity and gate-voltage tunability are the two main features of these devices. Positive MR behavior maintains up to room temperature but with a smaller magnitude about 300% for B=8T. On the other hand, a quadratic dependence of the resistivity R on magnetic field B is clearly observed at high carrier density where graphene performs similar to ordinary metals; however R depends super-linearly on B at charge neutrality point (CNP) which mainly originates from massless Dirac-fermions in graphene. All MR behaviors at various temperatures and gate voltages can be well interpreted by the combination of classical PL model and the quantum model. The large magnitude of positive MR with flexible controlled parameters (i.e. temperatures and carrier density) suggests great potential for novel applications such as magnetic sensors and ultrahigh density memory storage.
8:00 PM - P5.23
Directed Control of Carrier Type and Density in Ferroelectric-gated Graphene through Interface Engineering
Martin1 2, Moonsub
Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA; 2,
Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.Show Abstract
Graphene/ferroelectric hybrid structures - while showing exciting performance in terms of high mobility and the accessibility of distinguishable, nonvolatile resistance states - have not yet shown their full potential: the direct control of the carrier density and type in graphene through variation of the ferroelectric polarization. This control could provide new means of manipulating electron transport in graphene through complex ferroelectric gate structures. However, hysteresis effects observed in previous studies of graphene on ferroelectric oxide thin films have been attributed to effects other than the ferroelectric polarization, presumably the charging of interface states or charge redistribution facilitated through polar molecules at the interface. Here, we will discuss graphene/PbZr0.2Ti0.8O3 (PZT) hybrid structures that exhibit bidirectional interdependency between the graphene doping level and the ferroelectric polarization. This work was enabled by the development of a one-touch transfer process that allows for direct transfer of high-quality CVD grown graphene onto the ferroelectric film surface to ensure beneficial interfacial properties. Furthermore, as part of this work, we will discuss complete current-voltage and ferroelectric studies of graphene-contacted ferroelectric capacitors including evidence of symmetric current-voltage response and reversible ferroelectric polarization switching of epitaxial PZT thin films. Additionally we have completed detailed current-voltage studies of over 75 ferroelectric-gated graphene transistors and have observed that the manipulation of the polarization state of the ferroelectric gate oxide impacts both the carrier type and the density of carriers in the graphene. Additionally, we have established routes and gained insight into environmental factors that impact the process to the point where we can manipulate the carrier type from p- to n-type or even intrinsic as a response to the switching of the ferroelectric polarization. Detailed pulse-width- and time-dependent measurements have been used to separate the role of ferroelectric polarization effects from extrinsic charging or charge redistribution effects at the interface. This work is key to understanding prior studies and routes to utilization of ferroelectric-gated graphene for potential devices. Finally, we will also discuss our efforts on two-dimensional Raman mapping of graphene on ferroelectrics and photocurrent response in graphene devices on diverse ferroelectric domain structures.
8:00 PM - P5.25
Transfer of Graphene Devices to PLD Grown SrTiO3 Substrates
Physics, University of California, Riverside, Riverside, California, USA.Show Abstract
Single-layer graphene can be easily located on the surface of a Silicon wafer with 300nm SiO2 using optical microscopy. This may not be possible with other substrates of varying thicknesses. We have developed a technique for wet-etching the SiO2, peeling the device from the surface, and transferring it to any arbitrary substrate. The device has electrical leads already patterned onto the flake via Electron Beam Lithography (EBL) and metal is deposited for good electrical contact. This technique eliminates the need to locate the graphene flake on the target substrate and align to it for patterning using EBL. The completed device is then ready for any electrical measurements and a direct comparison can be made between the electrical transport properties of graphene on SiO2 and the target substrate. A device has been transferred from SiO2 to another SiO2 surface with no change in Dirac point position and only a small decrease in carrier mobility. This confirms that the transfer technique does not significantly degrade the quality the graphene flake. A graphene device has been transferred to a 250nm thick layer of Strontium Titanate (STO) that has been grown epitaxially on Nb-doped STO via Pulsed Laser Deposition (PLD). The STO layer, with a higher dielectric constant than SiO2 (approximately 2 orders of magnitude at room temperature) has a higher capacitance and produces a more effective graphene FET. The Dirac point can be swept through with a much smaller gate voltage range. A higher carrier mobility is expected with a graphene device on the surface of a material with a higher dielectric constant if charged impurity scattering is a primary limiting factor. Graphene devices transferred to 200μm thick STO substrates display a qualitatively similar behavior. Possible reasons for the absence of the high dielectric substrate effect on graphene carrier mobility will be discussed.
8:00 PM - P5.26
Three-Dimensional Graphene-based Assemblies
, Lawrence Livermore National Laboratory, Livermore, California, USA.Show Abstract
Graphene has shown the potential to significantly impact a number of different technologies, including energy storage. Properties such as high surface areas and electrical conductivity make it a promising material for hydrogen storage, battery, and ultra capacitor applications. One route to realizing the full potential of graphene in energy storage applications is the assembly of three-dimensional macroscopic graphene networks that retain the properties of individual graphene sheets. Herein we report the assembly of graphene sheets into a hierarchical architecture with length scales extending from the nanoscale to the macroscopic regime. These graphene macroassemblies are formed via cross-linking reactions between single- and/or few-layer graphene oxide sheets in suspension. The hierarchical structure possesses a number of novel properties including mechanical stiffness (up to 10 GPa) and electrical conductivities (up to 105 S/m) orders of magnitude higher than previously reported, surface areas that approach the theoretical values expected for a single graphene sheet (~2500 m2/g), and extraordinarily large mesopore volumes (up to 5 cm3/g). Energy storage behavior for capacitor and Li-ion battery applications were evaluated. The graphene-based electrode simultaneously exhibited high energy (~102 Wh/kg) and power densities (~102 kW/kg) in aqueous electrolytes (symmetric cell), while metal oxide-coated graphene electrodes exhibited large Li-ion capacities (~1000mAh/g). The details of the synthesis and characterization of these novel graphene assemblies will be presented.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DEAC52-07NA27344.
8:00 PM - P5.27
Microstructural Characterization in Rotated Double-layer Graphene Using Transmission Electron Microscopy
Yuk1 3 4, Hu Young
Jeong1 2, Na Yeon
Kim1, Mi Jin
Lee1, Jeong Yong
Lee3 4, Zonghoon
School of Mechanical and Advanced Materials Engineering, UNIST, Ulsan, Republic of Korea; 2,
UNIST Central Research Facilities, UNIST, Ulsan, Republic of Korea; 3,
Center for Nanomaterials and Chemical Reactions, Institute for Basic Science, Daejeon, Republic of Korea; 4,
Department of Materials Science and Engineering, KAIST, Daejeon, Republic of Korea.Show Abstract
By layer-by-layer stacking of various two-dimensional atomic crystals, it is possible to form multilayer heterostructures with designed electronic properties. Double-layer graphene, especially, has attracted considerable interest because their electronic, optical, and mechanical properties provide useful characteristics not obtainable in single layer graphene. A well-known example is opening tunable band gaps in Bernal-stacked bilayer graphene by applying transverse electric field, which makes them promising candidates for nanoelectronic devices. Even though these properties of double-layer graphene are radically varied depending upon their structures, including the stacking order, rotation-angle and defects, their microstructural characteristics and properties have not yet been studied in depth.
We present quick, accurate and large-area mapping of microstructures in double-layer graphene, such as grains, defects and stacking rotation-angles. We use dark-field transmission electron microscopy (DF-TEM) combining with scanning electron diffraction with a nanoparallel electron beam, as well as high-resolution TEM in Cs corrected Titan Cube operated at a low kV. Grains and defects in double-layer graphene are identified and visualized, because DF-TEM images are sensitive to the alignment between the electron diffraction angle and the crystal orientation. Our comprehensive TEM study provides crucial structural information of double-layer graphene, which is sincerely demanded for their future development in optoelectronic and nanoelectronic devices.
8:00 PM - P5.28
P-N Junction Formed on Graphene Steps: Homo- and Hetero- Cases
Electronic Engineering, The Chinese University of Hong Kong, Hong Kong, Hong Kong.Show Abstract
P-N junction is a fundamental building block in the modern electronic circuits. Previously, we have fabricated graphene p-n junctions by a one step inhomogeneously thickness-dependent surface treatment of mono-/bilayer graphene sheets. Here, in this presentation, we systemically study the attributes across the graphene p-n junction interface by means of Kelvin probe force microscopy (KPFM) and transport measurements. Interestingly, we find the junction behaves distinctly for different surface treatments. Through organic surface charge transfer doping, the junction is sharply transformed from p-type (mono-layer) region to n-type (bi-layer) region in terms of surface potential distribution. The total channel resistance fits well with the sum of two individual GFETs. Although the rectification effect is not observed due to the absence of additional resistance in the junction, the output characteristic presents an abnormal negative differential resistance (NDR) behavior, whose origin and its deep impact to RF application will be discussed elsewhere. Here we find that, in the case of covalent bond doping, i.e. by oxygen plasma irradiation, the surface potential transition regions of the junction span up to several hundred nanometers. And the rectification effect is clearly observed in the two terminal measurements.
We ascribe the distinct behaviors to the carrier density variation in different graphene systems; namely, under the condition of charge transfer doping, since the graphene basal plane is largely reserved, the relatively large carrier density results in a metal-to-metal like junction, and an equivalent series resistance. However, in the case of the oxygen plasma irradiation, the trap states limit the carrier density and therefore a long space charge region is formed, which produces a metal-semiconductor-like junction. Our results not only unveil the detailed properties of graphene p-n junction interface, but also gain an insight into its great potential in nano-electronic applications.
8:00 PM - P5.29
Properties of Graphene Antidot Lattices
Physics and Nanotech, Aalborg University, Aalborg East, Denmark.Show Abstract
The vanishing band gap of graphene severely restricts application in electronic and optoelectronic devices. Recently, graphene antidot lattices (GALs) have been suggested as a means of creating sizeable gaps. These structures are based on either periodic arrays of perforations [1,2] or patterned adsorption of hydrogen . The properties of both types of GALs are analyzed based on atomistic simulations (tight-binding, DFT and DFT based tight-binding) as well as continuum approaches. The influence of superlattice geometry on band gap is discussed and simple scaling laws are explained. Also, optical, magnetic and transport properties will be presented. Calculations are compared to recent experiments and the feasibility of GAL based electronic and optoelectronic devices is discussed.
1. T. Garm Pedersen, C. Flindt, J. Pedersen, A-P. Jauho, N.A. Mortensen and K. Pedersen “Graphene antidot lattices - designed defects and spin qubits”, Phys. Rev. Lett. 100, 136804 (2008).
2. J. A. Fürst, J.G. Pedersen, C. Flindt, N.A. Mortensen, M. Brandbyge, T. Garm Pedersen, and A-P. Jauho “Electronic structure of graphene antidot lattices”, New J. Phys. 11, 095020 (2009).
3. R. Balog, B. Jørgensen, L. Nilsson, M. Andersen, E. Rienks, M. Bianchi, M. Fanetti, E. Lægsgaard, A. Baraldi, S. Lizzit, Z. Sljivancanin, F. Besenbacher, B. Hammer, T. Garm Pedersen, P. Hofmann, and L. Hornekær, “Band Gap Opening in Graphene Induced by Patterned Hydrogen Adsorption”, Nature Materials 9, 315 (2010).
8:00 PM - P5.30
Current Status of Wafer Scale Graphene: Material and Electrical Studies
Mircoelectronics Research Center, The University of Texas at Austin, Austin, Texas, USA; 2,
, Aixtron Nanoinstruments, Cambridge, United Kingdom.Show Abstract
One of the most promising applications for graphene is to enable next generation nanoelectronics. This requires a CMOS compatible wafer-scale synthesis, characterization and transfer of graphene film, which remain quite challenging. Previously, we had synthesized high-quality monolayer graphene on hydrogen-rich Cu (111) film. In this study, we will report our recent progress to address outstanding challenges in wafer-scale characterization, transfer of graphene and device fabrication with enhanced performance.
Raman mapping and statistical analysis were performed using our developed software (GRISP available on nanohub), indicating a high uniformity (>97% coverage) of monolayer graphene with immeasurable defects (>95% defect-negligible) across a 100-mm wafer. The transfer of wafer-scale graphene is not straight forward because: 1) direct etching of copper in ammonium persulfate (APS) at this scale typically results in corrugated film stack of polymer coated graphene before release; 2) two-step etching process demonstrated before is time inefficient (>24 hrs) even with highest concentration of buffered oxide etcher (BOE). We found out that a small addition of BOE in APS could release wafer-scale polymer coated graphene film without corrugation and in a substantially shorter time (<8 hrs). Raman inspection of transferred graphene film showed uniform monolayer obtained on standard 285 nm SiO2/Si.
Over 40,000 graphene field effect devices (GFETs) were then fabricated on a 100-mm wafer covering an area of 70 ×70 mm2, including 2- and 4- point probes for various electrical characterizations using back-gate. Typical Id-Vg curve of as fabricated GFETs exhibited severely positive Dirac voltage and asymmetric hole/electron transport with poor electron mobility. After applying a 15 nm thick passivation layer of HfO2 with atomic layer deposition, the Dirac point was back-shifted with improved symmetry for both hole and electron branches. An extracted mobility of ~3,500 (up to 5,700) cm2/Vs was observed under ambient conditions. Similar to fluoropolymer passivation yielding improved transistor performance, our study reveals that appropriate dielectric capping can restore the intrinsic properties of graphene that is often degraded during the transfer process as other literatures also observed.
This study demonstrates recent progress in wafer-scale Raman inspection, improved transfer of graphene as well as 104-scale fabrication of GFETs with enhanced performance via dielectric passivation, ensuring key essentials to very large-scale integrated systems.
8:00 PM - P5.32
Impact of Point Defects in Graphene Systems
Martinez-Galera1, Jose Maria
Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Madrid, Spain.Show Abstract
Topological defects strongly influence the mechanical, electronic and even magnetic properties of low dimensional carbon-based systems. Taking advantage of the key role of defects in these systems, a unique route based on defect engineering is being developed to broaden the functionalities of graphene. In particular, vacancy-type defects are of an extraordinary importance as they are the key ingredient to understand the new properties shown by functionalized graphene after irradiation. While the role played by these vacancies as single entities has been extensively addressed by theory, experimental data available only refer to statistical properties of the whole heterogeneous collection of vacancies generated in the irradiation process. Scanning tunneling microscopy (STM) has great potential in this arena since it enables characterization of point defects at the atomic level.
In our work, we first created well characterized individual vacancies on graphene layers by Ar+ ion irradiation and then, using low temperature scanning tunneling microscopy and spectroscopy (UHV-LT-STM/STS), we individually investigated the impact of each type of such vacancies on the electronic, structural and magnetic properties of several graphene systems [1-3].
 M. M. Ugeda, I. Brihuega, F. Guinea and J. M. Gómez-Rodríguez, Phys. Rev.
Lett 104, 096804 (2010).
 M. M. Ugeda, D. Fernández-Torre, I. Brihuega, P. Pou, A. J. Martínez- Galera,
R. Pérez and J. M. Gómez-Rodríguez. Phys. Rev. Lett 107, 116803 (2011).
 M. M. Ugeda, I. Brihuega, F. Hiebel, P. Mallet, J. Y. Veuillen, J. M. Gómez-
Rodríguez and F. Ynduráin Phys. Rev B,85, 121402 (R) (2012).
8:00 PM - P5.33
Chemical Structure of Multilayer Oxidized Epitaxial Graphene: Experiments and Density Functional Theory Calculations
de Heer2, Yves
Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA; 2,
Physics, Georgia Institute of Technology, Atlanta, Georgia, USA; 3,
Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas, USA; 4,
Institute for Superconductors and Innovative Materials and Devices, National Research Council, Naples, Italy.Show Abstract
In this work, density functional theory
calculations are used to interpret new
X-ray photoelectron spectroscopy (XPS),
Infrared (IR) spectroscopy,
X-ray diffraction (XRD), and atomic force
microscope (AFM) measurements of the oxide
of epitaxial graphene. This layered carbon
material is obtained by Hummers oxidation
of 6- to 17-layer graphene films grown
epitaxially at high temperature
on a silicon carbide substrate.
Our measurements show that this form of
graphene oxide differs from the
conventional material obtained via the
standard oxidation, exfoliation, and
deposition method. In particular,
XRD shows that the film preserves the
layered structure and an excellent epitaxial
character, and shows interlayer distances
as large as 10 angstrom. XPS and IR
measurements concur in
showing a chemical structure based on
the presence of oxygen-functional groups
on the carbon basal planes and very little
amount of water molecules intercalated
in-between the layers. Further, AFM
measurements shows Young's moduli ranging
from 30 GPa up to 120 GPa. Extensive
density functional theory calculations
are carried out to address the complex
inverse problem posed by the aforementioned
measurements, attempting to elucidate the
molecular-scale feature of this novel
thin-film graphene-based material.
The calculations show that a most plausible
molecular structure for the oxide of
epitaxial graphene consists of mildly
oxidized graphene layers covalently bridged
by short polyoxymethylene chain.
8:00 PM - P5.34
Growth Structure and Work Function of Bilayer Graphene on Pd(111)
Materials Science and Engineering, UCLA, Los Angeles, California, USA; 2,
Mechanical Engineering, Colorado School of Mines, Golden, Colorado, USA; 3,
, Sandia National Laboratories, Livermore, California, USA.Show Abstract
Using in situ low-energy electron microscopy and density
functional theory, we studied the growth structure and work function
of bilayer graphene on Pd(111). Low-energy electron diffraction
analysis established that the two graphene layers have multiple
rotational orientations relative to each other and the substrate
plane. We observed heterogeneous nucleation and simultaneous growth
of multiple, faceted layers prior to the completion of second layer.
We propose that the facetted shapes are due to the zigzag-terminated
edges bounding graphene layers growing under the larger overlying
layers. We also found that the work functions of bilayer graphene
domains are higher than those of monolayer graphene, and depend
sensitively on the orientations of both layers with respect to the
substrate. Based on first-principles simulations, we attribute this
behavior to oppositely oriented electrostatic dipoles at the
graphene/Pd and graphene/graphene interfaces, whose strengths depend
on the orientations of the two graphene layers.
8:00 PM - P5.35
Direct Observation of Charge Migration in Progressively Reduced Graphene Oxide Using Electrostatic Force Microscopy
Gupta1, Pulickel M.
Ajayan2, Andrew M.
Dattelbaum1 3, Stephen K.
Doorn1, Aditya D.
Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, USA; 2,
Mechanical Engineering & Materials Science, Rice University, Houston, Texas, USA; 3,
Material Synthesis & Integration Devices, Los Alamos National Laboratory, Los Alamos, New Mexico, USA.Show Abstract
The discovery of graphene and the tremendous attention it received led to the discovery of graphene oxide (GO) that was obtained by exfoliating graphite oxide. To date, it is considered an easy method for large scale production of graphene. However, in the last few years, it has emerged as a “new old material” and has attracted tremendous attention from Material Scientists. This is largely because, GO provides an ideal platform to manipulate and control its chemical structure, optoelectronic properties and ionic conductivity for a wide range of applications for flexible electronics and optoelectronic devices such as photodetectors, photovoltaics, energy storage and biosensors. However, before its widespread incorporation for next generation applications, it is critical to understand the physical and electrical properties of GO that are highly dependent on the density and nature of functional groups on GO. Here, we have used electrostatic force microscopy (EFM) to inject and directly probe the migration of injected charge as the GO is progressively reduced to RGO. Our EFM results on GO flakes indicate that the injected charge is completely localized within the plane of GO. However, with increasing degree of reduction, the injected charge rapidly delocalizes over a few microns until it ends up at the edge of the flakes. The results suggest that as we go from GO to RGO, there are more percolating pathways of sp2 that are formed that act as conduits for charge migration. Our results are consistent with the quenching of fluorescence observed on individual flakes of GO measured as a function of increasing reduction of GO to RGO. We will combine EFM results with that of fluorescence imaging to monitor the preferential removal of each functional group on GO.
8:00 PM - P5.36
Large Area Mapping of Graphene Lattice Orientations
, University of Texas at Dallas, Richardson, Texas, USA; 2,
, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea.Show Abstract
The growth mechanisms of chemical vapor deposited (CVD) graphene on copper are still not fully understood. Looking at the lattice orientations of a graphene sheet reveals a jigsaw of grain structure and grain boundaries. Maps of these features can give scientists clues as to what occurs during the synthesis of these two-dimensional structures.
In our study, we utilize a transmission electron microscope (TEM) to create orientation maps. The data for these maps are extracted through selected area diffraction (SAD) patterns created by the graphene lattice, allowing TEMs with electron energies above the graphene knock-on voltage to follow the method without damage to the structure. The rotation of the pattern correlates with the orientation of the graphene, thus measurement of the pattern’s rotation obtains the lattice rotation. By combining the diffraction patterns taken across the whole area of the TEM sample, a map can be obtained. Increasing the number of diffraction patterns taken can increase the resolution of the maps and can also increase the size of the analyzed area to the millimeter scale. This results in a longer time to complete the process so the procedure was aided by custom software written to control the TEM for image acquisition and calculate the rotation of each pattern with minimal user interaction. The data is then plotted for visual representation.
The graphene samples that were mapped consist of a growth series that start as small, nucleated, cross-like islands that grow until their edges meet and the space between are filled in. The maps revealed that most of the islands are single-crystal with a few being bi-crystal which had lattices closely mis-oriented to each other by 30 degrees. The maps of the complete coverage samples expose the grain sizes and shapes. Statistics of the diffraction pattern rotations pulled from each sample and graphed show that the graphene lattice orientation has a bi-modal distribution preference on the copper’s crystal substrate.
This process was also applied to double-layer graphene sheets transferred onto TEM grids. The SAD of these samples consisted of two diffraction spots, one set for each layer. The software was changed to determine and plot the mis-orientation between the two lattices. It also distinguished between areas of none, single-layer, and double-layer graphene.
With maps that can show the grain structure, lattice orientations and lattice mis-orientations, this method can become a tool for scientists to better understand the synthesis of graphene.
Acknowledgments: This work was supported by SWAN (GRC-NRI), AOARD-AFOSR (FA2385-10-1-4066) and the World Class University Program (by MEST through NRF (R31-10026)).
8:00 PM - P5.37
Extreme Monolayer-selectivity of Hydrogen-plasma Reactions with Graphene
Diankov1 2, Michael
Physics, Stanford University, Stanford, California, USA; 2,
Chemistry, Stanford University, Stanford, California, USA.Show Abstract
We study the effect of remote hydrogen plasma on graphene deposited on silicon oxide. We observe strong monolayer selectivity for reactions with plasma species, leading to isotropic
hole formation in the basal plane of monolayers and etching from the sheet edges. For few-
layer graphene and HOPG, we observe qualitatively different effects of hydrogen plasma, with
hexagonal etch pits that indicate that etching is highly anisotropic. The etch rate displays a
pronounced dependence on sample temperature for monolayer and multilayer graphene alike:
etching proceeds very slowly at room temperature, peaks at 400 °C and is suppressed entirely
at 700 °C. We observe that applying the same hydrogen plasma treatment to graphene de-
posited on the much smoother mica substrate leads to very similar phenomenology as on the
rougher silicon oxide, suggesting that a factor other than substrate roughness controls the reactivity of
monolayer graphene with hydrogen plasma species. We use hydrogen plasma treatment to produce graphene structures, such as nanoconstrictions and nanoscrolls, and investigate their properties using Raman spectroscopy, including tip-enhanced near-field Raman, as well as low-temperature transport measurements. The study suggests new directions for the controlled manipulation of graphene properties.
8:00 PM - P5.38
Mapping the Misorientation Angle in Double Layer Graphene FETs Using Raman Spectroscopy
Razavi Hesabi1, Corey
Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA; 2,
Materials Scienec and Engineering, University of Texas at Dallas, Dallas, Texas, USA.Show Abstract
Graphene, a planar honeycomb lattice of close-packed carbon atoms, exhibits a linear electronic dispersion near Dirac K points where electrons behave as massless Dirac fermions . In the case of double layer graphene, depending on relative orientation of the layers, interlayer interaction might lead to the electronic band structure splitting. The valence and conduction bands in a Bernal stacked graphene bilayer split into two parabolic branches near the K point. The splitting originates from the interaction of π electrons, leading to the opening of a band gap in bilayer graphene . While a zero band gap limits the application of monolayer graphene FETs due to a low on/off ratio, Bernal stacked bilayer graphene with a tunable band gap is a promising candidate to improve efficiency of graphene FETs . Deviation from Bernal stacked orientation is theoretically shown to affect band structure and consequently electronic properties. For industrial applications, the ability to map and control the misorientation angle between layers will be necessary to achieve the desirable electrical properties of the graphene devices. This work presents a method for systematically determining the misorientation between two layers on a wafer scale through the use of Raman spectroscopy. The validity of developed method and obtained misorientation maps will be confirmed by TEM study.
1. Y. Hao et al., Small 6 (2010)
2. L.M. Malarda et al., Physics Reports 473 (2009)
3. B. Fallahazad et al., Phsycal Review B 85 (2012)
8:00 PM - P5.39
Direct Measurement of the Intrinsic Dirac Point of Graphene
Xu2 1, Caifu
Zhang2 4, Rusen
Yan2 4, Peide
Electrical Engineering, Purdue University, West Lafayette, Maryland, USA; 2,
, National Institute of Standard and Technology, Gaithersburg, Maryland, USA; 3,
, University of California, Los Angeles, California, USA; 4,
, University of Notre Dame, Notre Dame, Indiana, USA.Show Abstract
Emerging as a promising and multifaceted material with fascinating electronic properties, such as high carrier mobility in the order of 105 cm2/Vs, graphene has attracted an immense amount of interest from all related disciplines since the pioneering work of Novoselov et al. in 2004. Fundamental knowledge of the physical properties of graphene and the physical mechanisms governing the electrical operation of graphene-based devices has grown dramatically. With the recent success of large area chemical vapor deposition (CVD) growth of graphene, industrial applications such as transparent electrodes, field effect transistors (FETs), and quantum well devices are becoming more promising. Surprisingly, there is little information on the intrinsic electronic band alignment of the graphene/oxide interface to date, despite its pivotal role in the design, fabrication, and characterization of graphene-based devices.
We report the first direct measurement of the Dirac point, the Fermi level, and the work function of graphene by performing internal photoemission measurements on a graphene/SiO2/Si structure with a unique optical-cavity enhanced test structure. A complete electronic band alignment at the graphene/SiO2/Si interfaces is established. The observation of enhanced photoemission from a one-atom thick graphene layer was possible by taking advantage of the constructive optical interference in the SiO2 cavity. The photoemission yield was found to follow the well-known linear density-of-states dispersion in the vicinity of the Dirac point. At the flat band condition, the Fermi level was extracted and found to reside 3.3 eV ± 0.05 eV below the bottom of the SiO2 conduction band. When combined with the shift of the Fermi level from the Dirac point we are able to ascertain the position of the Dirac point at 3.6 eV ± 0.05 eV with respect to the bottom of the SiO2 conduction band edge, yielding a work function of 4.5 eV ± 0.05 eV which is in an excellent agreement with theory. The accurate definition of the work function of graphene is of significant importance to the engineering of graphene-base devices and the measurement technique we have demonstrated in this talk would find numerous applications in other 2-Dimensional material systems.
 Geim et al., Nature Materials 6 (3): 183-191.
 Novoselov et al., Science 2004, 306, 666-669.
 Das Sarma, et al., Rev. Mod. Phys. 2011, 83, 407-470.
 Kim, et al., Nature 2009, 457, 706-710.
8:00 PM - P5.42
Graphene Metallization of High-stress Silicon Nitride Resonators for Electrical Integration
van der Zande3 4, Gwan-Hyung
Department of Electrical Engineering, Columbia University, New York, New York, USA; 2,
School of Applied and Engineering Physics, Cornell University, Cornell University, Ithaca, New York, USA; 3,
Energy Frontier Research Center, Columbia University, New York, New York, USA; 4,
Department of Mechanical Engineering, Columbia University, New York, New York, USA; 5,
Cornell NanoScale Science & Technology Facility, Cornell University, Ithaca, New York, USA.Show Abstract
A resonator is an essential component to modern electronics, most often used as a filter or an oscillator. One of the key requirements for a good resonator is high quality factor, which conventional electronic filters have failed to meet. Recently, stoichiometric silicon nitride resonators have become popular for their extremely high quality factor, which originates from the high stress they possess . However, the insulating nature of the material has hindered its broader implementation. Attempts have been made to metalize the silicon nitride membrane by depositing thin layer of metal on top. However, it was found that such metal deposition results in degradation of the quality factor [2, 3] - by more than a factor of four when for only 5nm of chrome .
In this work, we show that graphene can be used as a conductive coating for SiN membranes without reducing the quality factor. We first demonstrate the fabrication of these Silicon Nitride - Graphene (SiNG) hetero-structure resonators. CVD graphene grown on copper foil is coated with PMMA on which PDMS is placed. After the copper etch, remaining graphene/PMMA/PDMS stack is placed on top of the silicon nitride resonators. Readily upon heating, PDMS delaminates, and final H2/Ar anneal removes the PMMA leaving only the silicon nitride and graphene.
Examining the quality factors of silicon nitride resonators with and without graphene on top using a piezo-drive - optical detection scheme, we have found that the quality factor degradation of silicon nitride resonator due to the added graphene layer is negligible, often within the margin of measurement errors. Furthermore, we have not only electrically actuated SiNG resonators using global silicon back-gate, but also tuned the resonators by changing the gate bias, while optical interferometry was used for detection. The highest quality factor measured on SiNG resonator using electrical drive was around 250,000 for the n1s1 mode of a 163µm diameter drum, while the tunability was about -2% per 10V. We have observed capacitive softening in the tuning curve, due to the highly stressed silicon nitride (~0.5%). We were also able to measure the displacement current-induced dissipation and found good agreement with an earlier study .
 “A megahertz nanomechanical resonator with room temperature quality factor over a million” S. S. Verbridge, et al., APL., 2008
 “Nanomechancial resonant structures in silicon nitride: fabrication, operation and dissipation issues”, L. Sekaric, et al., Sens. Actuators, A, 2002
 “Control of Material Damping in High-Q Membrane Microresonators”, P.-L. Yu, et al., PRL., 2012
 “Stamp Transferred Suspended Graphene Mechanical Resonators for Radio Frequency Electrical Readout”, X. Song, et al., Nano Lett., 2012
8:00 PM - P5.43
Easy Graphene Transfer Method by Using `Crystalbond'
Kim1, Yun Jeong
Hwang3, Gyu Tae
, Korea University, Seoul, Republic of Korea; 2,
, Trinity College Dublin, Dublin, Ireland; 3,
, Korea Research Institute of Standards and Science, Daejeon, Republic of Korea.Show Abstract
A new graphene transfer method using 'crystalbond' was devised by thermal recipes for bonding and releasing. Graphenes could be transferred to any specific location of the substrate in a large scale more simply and faster than the previous methods such as a scotch-tape method or the PMMA transfer method.
The transferred graphene was characterized by Raman spectroscopy and optical microscope image, confirming the good quality of the graphene during the transfer processes. Dirac points of transferred graphene were identified and characterized in a configuration of field effect transistor, indicating the good electrical property of the transferred graphene. The easy processes enable successive thermal stampings for local transfers of selected region of the graphene layer.
8:00 PM - P5.44
Simple Soft Lithographic Patterning Method of Graphene Sheets
, KRICT, Daejeon, Republic of Korea; 2,
, Korea University, Seoul, Republic of Korea; 3,
, Sungkyunkwan University, Suwon, Republic of Korea.Show Abstract
It is essentially important to develop suitable graphene patterning process for future industrial applications. Especially, transfer or patterning method of CVD-grown graphene has been studied. we eport simple soft lithographic process to develop easily applicable patterning method of large-scale graphene sheets by using chemically functionalized polymer stamp. Also important applications, capacitors with graphene electrode and commercial polymer dielectrics for the electrostatic-type touch panel are fabricated using the developed soft lithographic patterning and transfer process.
8:00 PM - P5.45
Synthesis and Characterization of Boron-doped Multi-walled Carbon Nanotubes with Application to Supercapacitors
Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan; 2,
Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, 31040, Taiwan; 3,
Institute of Polymer Science and Engineering, National Taiwan University, Taipei, 10617, Taiwan.Show Abstract
The electrochemical supercapacitor (SC) has received increasing attentions due to its high power density (10 kW kg-1), short charge/discharge duration (in seconds), long cycle life (over a million cycles), and environmental friendliness. Recently, boron-doped carbon has been researched as supercapacitor electrode materials because of the high specific surface area of carbon and the modified electronic structure which would result in the improved electrical double layer capacitance and pseudocapacitance by doping boron.
In this study, multi-walled carbon nanotubes (MWCNT) was doped with different concentrations of boron precursor, i.e., 0.5%, 2%, 10%, and 20%, by a chemical method. The bare MWCNT and boron-doped MWCNT with various concentrations were proposed as the materials for SC applications. The SC with 2% boron-doped MWCNT shows better specific capacitance and charge/discharge ability as compared with other cases. The specific capacitances of 9.75, 16.93, 66.49, 38.30, and 31.8 F/g were obtained from cyclic voltammetry at a scan rate of 5 mV/s for the SC with bare MWCNT, 0.5%, 2%, 10%, and 20% boron-doped MWCNT, respectively. Moreover, the SC electrode with 2% boron-doped MWCNT exhibits good stability and the capacitance retains even after 1,000 galvanostatic charge/discharge cyclings, suggesting its potential as the SC material.
8:00 PM - P5.46
Graphene Oxide-supported Two-Dimensional Microporous Polystyrene
, Materials Science Institute, Guangzhou, Guangdong, China.Show Abstract
Graphene, with a single layer plane structure, has amazing electrical and mechanical property, such as high electro conductibility, flexibility, stiffness. This unique structure has rendered graphene highly promising for various applications in energy storage, electronic device. To further explore new functions for graphene, the construction of macroscopic architectures using graphene as the building block has been well performed. 0-dimensional, two-dimensional and three-dimensional macrostructure have been constructed via vacuum filtration, layer-by-layer (LBL) assembly and chemical vapor deposition (CVD). Recently, great effort has been focused on porous graphene materials, Taking advantages of both the graphene composition and the pore structures, porous graphene materials have great application potentials in various fields. Three-dimensional porous graphene materials with high surface area have been prepared by LBL assembly. However, the design and preparation of graphene/ microporous structure is still empty.
In this paper, a porous graphene oxide/polystyrene (GO/PS) was designed and prepared as follows: At first, a molecularbrush of PS was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP) from GO surface. Then, the GO/PS plane molecularbrush obtained was crossrlinked by carbon tetrachloride and a graphene oxide supported-microporous polystyrene was obtained. The SI-ATRP and crosslinking conditions were optimized in this work. The structures of the molecularbrush of PS and the related crosslinking GO/PS were determined by FTIR, TG, SEM and nitrogen adsorption-desorption analysis. The experimental results showed that PS molecularbrush were successfully grown on to the surface of GO. After crosslinking, the PS component was crosslinked into many round nanoparticles with a diameter of 20-30 nm, and therefore the specific surface area of GO/PS obviously increased. This kind of porous GO/PS composite was promising for the application in adsorption-desorption energy storage areas.
8:00 PM - P5.47
Surface Energy Engineered, High-resolution Micropatterning of Reduced Graphene Thin Films
Kim1, Beom Jun
Kim2 3, Yeongun
Ko1, Sung Tae
Song1, Na Rae
Lee1, Seung Wook
Jang1, Jeong Ho
Cho2 3, Suk Tai
Chemical Engineering and Materials Science, Chung-Ang University, Seoul, Republic of Korea; 2,
SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, Republic of Korea; 3,
Chemical Engineering, Sungkyunkwan University, Suwon, Republic of Korea.Show Abstract
We report a new approach for the fast and reproducible patterning of high-resolution reduced graphene oxide (rGO) microstructures over large area directly on rigid or flexible substrates. Such well-defined rGO micropatterns are created by modulating the surface energies of rGO thin films and pre-patterned elastomeric molds with the assistance of oxygen plasma. This technique offers the production of various shaped and sharp-edged rGO microstructures with a uniform thickness in the nanometer-scale. This plasma enhanced detachment patterning technique is extremely simple, effective, and easy to scale for large area rGO micropatterns without any pressurization and/or heating. The principle of our new patterning technique for the rGO microstructures is successfully explained based on the quantitative investigation of the work of adhesion between mold/rGO and rGO/substrate interfaces with the in-depth characterization of the high-resolution rGO micropatterns. As a demonstration of this patterning technique, we have successfully fabricated high performance top-contact organic field-effect transistors (OFETs) based on the rGO micropatterns as source-drain electrodes. Our patterning technique described in this manuscript shows great promise for making future graphene-based electronic devices
8:00 PM - P5.49
Interaction of Water Molecules with Epitaxial Graphene
Department of Physics, University of Erlangen-Nürnberg, Erlangen, Germany.Show Abstract
Graphene devices operated in ambient conditions are exposed to a variety of small molecules. These molecules act as dopant altering the electronic properties of graphene and interact strongly with defect sites. For example on ruthenium, it was shown that line defects in graphene are extremely fragile toward chemical attack by water, which leads to splitting of the graphene film into numerous flakes, followed by water intercalation under the graphene.
Here, we discuss the interaction of water molecules with epitaxial graphene on 6H-SiC(0001) based on low temperature scanning tunneling microscopy experiments. Epitaxial graphene on 6H-SiC(0001) allows us to compare water wetting with respect to the number of graphene layers. Distinct differences in the water adsorption structures of the interface layer compared to single and multiple graphene layers on SiC were observed. While the water clusters on graphene were influenced by the underlying graphene superstructure, larger water agglomerates were observed on the interface layer. Along defects, the graphene fractured occasionally into nanometer-sized flakes.
 F. Schedin et al. Nat. Mater., 6, 652-655 (2007).
 X. Feng, S. Maier, M. Salmeron, J. Am. Chem. Soc. 134 (12), 5662-5668, (2012).
8:00 PM - P5.50
Gauge Fields for Rippled Graphene Membranes under Central Mechanical Load
Physics, University of Arkansas, Fayetteville, Arkansas, USA; 2,
Materials Science, University of Utah, Salt Lake City, Utah, USA; 3,
Mechanical Engineering, Universidad del Norte, Barranquilla, Colombia.Show Abstract
Discussions of gauge fields on graphene are invariably given within continuum elasticity and there has been no discussion of when such approach breaks down. Expressions for gauge fields are then derived from a Hermitian electronic hamiltonian. This requirement translates into explicit conditions for atomic displacements that must be met at each unit cell. Following an approach where the atomic positions play the preponderant role, we develop an atomistic theory of strain on graphene, where all relevant quantities -including gauge fields- are directly expressed in terms of atomic displacements only. Using this approach we study suspended (rippled) graphene membranes under load by a sharp tip. In addition to the pseudo-magnetic field we also compute the deformation potential, which acts as an on-site potential energy. We observe that the deformation potential -neglected without proper justification in many published works- can modify the electronic spectrum dramatically in qualitative ways. Discussion of relevant experiments will also be given.
8:00 PM - P5.51
A Study of Stacking Order in Double-layer Graphene
Materials, Imperial College London, London, United Kingdom; 2,
, Elettra, Sincrotrone Trieste S.C.p.An, Trieste, Italy.Show Abstract
Chemical vapor deposition of graphene on copper is a promising method towards large area synthesis of high quality graphene. The growth of bi/few layer graphene can also be achieved on copper substrates and ontrol over coverage and stacking order can enable growth of AB versus AA stacked double layer graphene over large areas. Here we have investigated the stacking order of double layer graphene in correlation with growth conditions and the crystal orientations of copper. Toward this end, we have analyzed graphene grown on a variety of Cu crystal orientations [e.g. Cu(100), Cu(111), Cu(211), and Cu(310)] at different temperatures and methane/hydrogen gas pressure ratios. In-situ low-energy electron microscopy/diffraction (LEEM-LEED) characterization and Raman spectroscopy analysis reveal the presence of AA, AB stacking order as well as twisted bilayer graphene. Evidence for AA stacking has been also confirmed by micro- ARPES (angle resolved photoemission spectroscopy) performed on single and double layer graphene as well as by cross-sectional HRTEM imaging. Statistical distribution analysis shows that half of the double-layer graphene areas are AB stacked and correlation with the Cu crystal orientation is discussed.
8:00 PM - P5.52
Morphology Effects on Electrical Properties of Advanced Graphene Aerogels
Fan1, Daniel Zhi Yong
Tng1, Truong Son
Feng1, Hai Minh
Mechanical Engineering, National University of Singapore, Singapore, Singapore.Show Abstract
Three-dimensional self-assembled graphene aerogels have been fabricated by mild chemical reduction method with L-ascorbic acid. The effect of graphene oxide concentrations, reduction agents and synthesis conditions (reduction temperature and reduction time) on the morphologies and electrical properties of the as-prepared graphene aerogels was systematically investigated. A simple but effective method controlling large specific surface area, pore volume, pore size and electrical conductivity of the graphene aerogels was achieved. After the annealing treatment at 400°C for 5h under Ar environment, the electrical properties of the developed graphene aerogels are significantly improved. The experimental results of this study are very useful for energy storage applications as the performance of graphene aerogel-based electrodes strongly depend on the morphology and electrical properties of the graphene aerogels.
8:00 PM - P5.53
Simulations of STM Images of Graphene on Si(111)
MicroEP, University of Arkansas, Fayetteville, Arkansas, USA; 2,
Physics, University of Arkansas, Fayetteville, Illinois, USA; 3,
Beckman Institute, University of Illinois, Urbana, Illinois, USA.Show Abstract
We have studied, within density-functional theory in the LDA approximation, the structure of graphene placed on a Si(111) substrate to understand the atomic scale graphene-substrate interaction. We accomplished this using the SIESTA package on computational facilities at The University of Arkansas. Electronic wavefunctions are obtained from the code. We developed our own program to set an integration range and add up the densities for all points in a real-space mesh from each wavefunction at a dense k-point mesh. The program generates simulated STM images which are compared to experimental ones showing reasonable agreement.
This is an important study because of the widespread use of graphene and Si wafers in research and their potential use in large commercial scale operations. Understanding the electronic and topographic properties at this interface is important for integrating graphene into future nanoelectric devices.
8:00 PM - P5.54
Non-equilibrium between Energy Carriers in Laser-irradiated Graphene
ME, Purdue University, West lafayette, Indiana, USA; 2,
ME, University of Texas Austin, Austin, Texas, USA; 3,
, Intel Corporation, Portland, Oregon, USA; 4,
UM-SJTU Joint Institute, Shanghai Jiao Tong University, Shanghai, China.Show Abstract
Graphene has attracted extensive attention due to its exceptional thermal and electronic properties. Its gapless semi-metallic nature leads to significant electron-phonon (e-ph) interactions near the Dirac point at room temperature. Raman spectroscopy is typically used to characterize graphene in experiments and also to measure properties like thermal conductivity and optical phonon lifetime. The laser-irradiation processes underlying this measurement technique include coupling between photons, electrons and phonons. Recent experimental studies have shown that e-ph scattering limits the performance of graphene-based electronic devices due to the difference in their timescales of relaxation resulting in various bottleneck effects. Furthermore, recently published thermal conductivity measurements on graphene are sensitive to the laser spot size which indicates the existence of non-equilibrium between various phonon groups. These studies point to the need to study the spatially-resolved non-equilibrium between various energy carriers in graphene. In this work, we propose a diffusive multi temperature model which includes all significant energy carrier transport and interaction processes including diffusion, e-ph and ph-ph interactions, and apply the model to single layer graphene under laser irradiation. Electron cooling through phonon emission is computed from density functional theory (DFT) in terms of the net phonon generation rate, whereas the interactions between various phonon groups are modeled in terms of a relaxation time approximation using the parameters obtained from lattice dynamics (LD). Using our model, we obtained the spatially resolved temperature profiles of all relevant energy carriers throughout the entire domain; these are impossible to obtain through experiments. Our results clearly show the difference in temperature distribution of various carriers at steady state conditions within the hot spot. Our results indicate that experimental measurements could under-predict the lattice thermal conductivity if this non-equilibrium were disregarded.
8:00 PM - P5.55
Transmission Electron Microscopy and Tomography Characterization of Carbon Nanostructures from Industrial Nanocomposites
Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, USA; 2,
, FEI Company, Hillsboro, Oregon, USA; 3,
, Applied NanoStructured Solutions, LLC, Baltimore, Maryland, USA.Show Abstract
A promising application of carbon nanostructures (CNS) - such as stacked cones, multi-walled, single-walled or entangled nanotubes, etc. - is in nanocomposites for high performance structural materials. One class of material suitable for nanocomposite production comprises CNS grown directly on micrometer-scale diameter glass or carbon fibers. Fibers coated with catalyst particles pass through a growth chamber and a forest of CNS forms on the surface of the fibers. Process parameters can be adjusted to produce CNS of different length, density and interconnectedness. These materials can be processed in the same way as conventional fiber-reinforced composites by infusing them with an epoxy matrix. Transmission electron microscopy (TEM) imaging is generally employed to obtain the structure and morphology of the CNS. However, statistical analysis of carbon nanotube “forests” can be challenging, especially when applications involve CNS which are not grown normal to the substrate fiber. The detailed arrangements - dispersion, clustering, bundling, networking, etc. - of the CNS within the composite can have a dramatic effect on the material’s bulk properties.
In this study, two distinctly different networks of CNS were characterized: one was grown on carbon fibers, the other on glass fibers. The CNS grown on the carbon fiber substrates consisted predominantly of single, multi-walled nanotubes. The CNS grown on the glass fiber substrates had a tendency to form bundles of multi-walled carbon nanotubes. Detailed statistical analyses of the number of walls, tube diameters and the number and diameter of any CNS bundles formed were obtained from high resolution TEM. TEM tomography was then applied to further resolve the three-dimensional complexity and confirm the connectivity of the CNS. We show that bright-field images combined with tomography and energy-filtered TEM can be used to obtain information about the 3-D network of CNS in high-performance structural composites.
8:00 PM - P5.56
Pressure Dependent Surface Graphitization on SiC (0001)
AFRL/RXAN, Air Force Research Lab, Wright-Patterson Air Force Base, Ohio, USA.Show Abstract
Low dimensional carbon nano-materials, such as two-dimensional graphene, one dimensional carbon nanotubes (CNTs), and zero dimensional C60, have made significant impacts in exploring novel properties, designing new functionalities, and enhancing performance of materials. Graphene is defined as one atomic layer of sp2 bonded carbon atoms arranged in a hexagonal lattice structure. CNTs are graphene sheets rolled-up into cylinders. Metal-free and well aligned CNTs and graphene are produced on SiC by surface thermal decomposition and graphitization at high temperatures under vacuum. However, the detailed atomic mechanisms of CNTs and graphene growths and their conversion are still subjects of investigation. Temperature effects on carbon nanostructural growth on SiC have been well studied, but the pressure effects are not well understood.
In this study, we have investigated the pressure effects on low dimensional carbon nanostructural growths on SiC surface at high temperatures. Generally, pressure reduction results in increasing surface graphitization rate of SiC, and conversion of lateral graphene to vertical CNTs structures. As the pressure is gradually reduced from ambient pressure to a few torr in Argon at 1700°C, the Raman scatterings at 292 and 388 cm-1 indicate the formation of single- walled carbon nanotubes (SWNTs) at a reduced pressure. Further, 2D bands shifts to low frequency at lower temperatures, indicating weak interactions between SiC lattices and carbon nanostructures on the surface. The kinetic behavior of SiC surface graphitization is analyzed. The study provides experimental evidences that graphene and CNTs growth and their interactions with SiC lattices could be kinetically controlled.
8:00 PM - P5.60
Electronic Transport Hysteresis due to Electron Irradiation in Graphene Field Effect Transistors
Department of Physics and Astronomy, Texas A&M University, College Station, Texas, USA; 2,
WPI-Advanced Institute for Materials Research, Tohoku University, Sendai, Japan.Show Abstract
We present the characteristic electronic transport behavior of graphene field effect transistor (FET) devices due to electron irradiation with various electron dosages at room temperature and in high vacuum. Graphene FET devices were fabricated by mechanical exfoliation and transferred onto silicon wafers covered with a 285nm thick oxide. The pristine devices showed p-type doping behavior, and no hysteresis was measured after they were loaded in high vacuum. When electrons with energies ranging from 1keV to 30keV were irradiated on graphene, the electrical transport properties showed a hysteresis and the devices exhibited n-type behavior. It is known that carbon nanotube and graphene FET devices show hysteresis in ambient condition. Dipolar molecules (e.g. water) surrounding FET devices are considered as one of the causes of the hysteretic behavior because they generate trapped charge carrier states. The hysteresis is typically reduced or entirely disappears in vacuum. We find results in agreement with other groups that the hysteresis measured in ambient condition disappears in vacuum. Upon electron irradiation in high vacuum, however, we observed a reappearance of the hysteresis which was observed for extended times in high vacuum. In addition, we studied the dynamic behavior of a shift of the Charge Neutral Point (CNP) versus time. Immediately following irradiation, the CNP shifts to a negative value. As time progresses, it then increases slowly without reaching the value prior to irradiation. Furthermore, we will present the dependence of conductivity on irradiation dosage. When the electron dosage was comparable to typical values used in electron beam lithography, no significant reduction in electronic mobility was observed indicating that this level of irradiation is a benign processing technique for graphene FETs.
8:00 PM - P5.62
Water Adsorption on Epitaxial Graphene: Unexpected Strong Reactivity of Line Defects
Feng1 2, Miquel
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA; 2,
Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, USA.Show Abstract
Epitaxial graphene on metal substrates has been demonstrated as a promising route for graphene synthesis. The graphene produced in this manner however is typically polycrystalline, with defects that can affect its properties. The impact of defects could be crucial when graphene interacts with adsorbed molecules due to their enhanced reactivity, so there is a need to understand the adsorption of environmentally abundant molecules, such as water and oxygen. Here we report a study of water adsorption on epitaxial graphene grown on Ru and Cu substrates using scanning tunneling microscopy (STM). We found that on Ru(0001), graphene defects are extremely fragile towards chemical attack by water, which splits the graphene film into numerous fragments at temperatures as low as 90 K, followed by water intercalation under the graphene. On Cu(111) water can also split graphene but far less effectively, indicating that the chemical nature of the substrate strongly affects the reactivity of the C-C bonds in epitaxial graphene.